I don't know if this counts as ``heavily'', but many buffering and
queueing schemes rely on modulo arithmetic. In some applications,
buffering and queuing are a substantial part of the total execution time.
Examples include some kinds of simulation and real-time event processing.

>[Please reply by news.]

Well, OK, but it's nice when the original poster will summarize,
particularly when I'm replying with these ``I don't know if this is
what you mean'' kinds of answers.